1. Field of the Invention
This invention relates to aqueous bleach, cleansing or disinfectant compositions of enhanced stability containing a hypohalite, e.g., sodium hypochlorite, and an effective amount of an N-containing heteroaromatic compound which is stable in the presence of said hypohalite and which is capable of forming multidentate complexes with copper ions present in said composition.
2. Description of Related Art
Alkali or alkaline earth metal hypohalites, most notably sodium hypochlorite, are among the strongest classes of bleaching agents known. Sodium hypochlorite is generally formulated with water at a concentration of less than about 15% by weight for use as a household bleach for laundering or for pulp and textile bleaching. It is also used as a cleansing adjunct in liquid cleaning compositions, e.g., dishwashing liquids, or as a germicide in disinfectant solutions, generally at concentrations of less than about 5% by weight.
One of the major problems associated with the use of these materials is the relative instability of aqueous hypohalite solutions. It is known that aqueous hypochlorite (OCl.sup.-) will decompose to chlorate (Cl0.sub.3.sup.-) when subjected to higher temperatures, e.g., above 40.degree. C., or after prolonged exposure to light. It is also known that the presence of heavy metal ions, e.g., copper, nickel and/or cobalt, in aqueous hypochlorite solutions will catalyze hypochlorite decomposition to oxygen gas and chloride ions. To maintain efficacy, manufacturers of products containing hypochlorite take steps to remove as much as possible of the heavy metal contaminants from the formulations and to provide appropriate packaging materials, storage and use instructions.
However, there are many uses of aqueous hypochlorite where the presence of or introduction of heavy metal decomposition catalysts is beyond the manufacturer's control. Such is the case with respect to concentrated aqueous hypochlorite bleach which is formulated to be diluted by the consumer with water prior to household or industrial use. Storage of unused diluted product can gradually lead to decreased bleaching efficacy and a build up of oxygen pressure in sealed containers as a consequence of the decomposition catalysed by heavy metal contaminants introduced with the dilution water. In addition, detergent and disinfectant compositions containing hypochlorite can be contaminated with heavy metals by contact with metal surfaces during manufacture or as a consequence of the presence of heavy metal in other ingredients present in the formulation such as bases, polyphosphates and pyrophosphates used as builders in dish washing liquids. Container pressurization by the oxygen released in the metal-catalyzed decomposition of hypochlorite can eventually create a hazard as a consequence of container rupture and leakage.
The prior art has recognized that the inclusion of one or more sequestering agents in washing or bleaching solutions containing a hypohalite or other oxidizers can retard the rate of hypohalite decomposition. The agent serves to sequester free heavy metal ions present in the solution thereby theoretically preventing or retarding their action as decomposition catalysts. Examples of such sequestering agents are disodium ethylenediaminetetraacetic acid, trisodium nitrilo triacetate, sodium gluconate and tetrasodium methylenediphosphonate as disclosed in U.S. Pat. No. 3,297,578; 2-hydroxy-3-aminopropionic acid derivatives as disclosed in U.S. Pat. No. 5,112,530; organic hydroxy carboxylic acids such as tartaric acid or inorganic acid salts such as sodium tellurate as disclosed in U.S. Pat. No. 4,474,677; and amino sulfonic acids such as disclosed in U.S. Pat. No. 2,730,428. Most of these compounds are added to the hypochlorite solution immediately prior to use and remain effective only for periods of hours or days, either because the strong oxidative effects of hypochlorite results in their eventual decomposition and loss of effectiveness as sequestering agents or they eventually react with and decompose the hypohalite.
U.S. Pat. No. 3,749,672 discloses an aqueous hypohalite bleaching composition also comprising an equilibrium mixture containing an N-hydrogen compound and the corresponding N-halo reaction product of hypohalite and N-hydrogen compound, stabilized at a pH of 4 to 11 using a mild acidic buffer.
U.S. Pat. No. 4,898,681 discloses dilute aqueous hypohalite solutions which are said to be stable over a period of many months containing the calcium chelate of disodium ethylenediaminetetraacetic acid (EDTA) as a stabilizer. It is speculated in this disclosure that enhanced stability is due to the unique resistance of this material to the oxidizing attack by hypochlorite when compared with the tetrasodium EDTA analog.
In addition, Japanese publication J6-2205-199 discloses that the problem of oxygen generation in closed containers containing hypochlorite bleach is prevented by formulating the composition with a mixture of an oily, oxygen-capturing agent which is an aromatic or aliphatic alcohol, aldehyde or ketone, a surface active agent and an alkaline stabilizer.
While these and other stabilizers may be effective to varying degrees, it has been found that many must be present in the hypochlorite composition in fairly significant amounts to be effective and their presence at these levels may detract from the bleaching/cleansing properties of the composition. In addition, many sequesterants are effective stabilizers only with respect to decomposition catalyzed by certain heavy metal ions present in the hypochlorite solution, e.g., cobalt or nickel, and may be ineffective against copper.